A field experiment was conducted to evaluate the potential of foliar treatment of phenylalanine or methionine with different concentrations (0, 50, 75, 100 mg/l) for improving growth characters, seed yield quantity and quality and some biochemical aspects of flax cultivars (Vaiking & Giza 8) under water deficit (skipping irrigation) grown in sandy soil during the two successive winter seasons of 2015/2016 and 2016/2017. Exogenous application phenylalanine or methionine led to marked increases in growth characters (shoot and root height, fresh and dry weights) compared to untreated plants. Concomitantly with an increase in the levels of IAA, photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), phenol, total soluble sugars, polysaccharides, and total carbohydrates as compared with the control. All treatments increased seed yield and its components, as) plant height, technical length, fruiting zone length, number of fruiting branches/plant, number of capsules/plant, also, biological yield /plant, seed yield /plant, 1000 seeds weight, biological yield /fed, seed yield /fed, straw yield /fed, seed oil % and oil yield (kg/fed) (when compared with the untreated controls. Also a marked increase in nutritional values of the seed yield and oil %. The maximum increases were obtained in response to application of methionine at 100 mg/l in both cultivars. These results suggest that there was a noticeable cultivar difference among tested cultivars. In general the flax cultivars were significantly different in their seed and oil yields due to application of these amino acids treatments. The highest seed and oil yields were recorded with Vaiking cultivar, while Giza-8 cultivar produced the highest straw yield under the same foliar application treatments.